Know your enemy: How to outfox the wily red fox

Peter d’Plesse

Stalking slowly through long grass beside a river channel, the foxes launched themselves from under a log. One went left and the other to the right. The first touch of the Brno’s rear trigger delivered a load of SG towards the first.

The same trigger caught the second with a 7mm bullet as it hesitated on the edge of the channel. The Brno combination performed as intended, snap shooting feral game in thick cover.

While I respect the abilities of feral game, their environmental impact must be controlled. Hunting provides an effective management strategy without the ethical issues of trapping and poisoning. Understanding the abilities of feral game helps give the hunter an edge. It can also explain why particular hunting tactics have proved effective over time.

Foxes are superb hunters with finely tuned senses to detect and catch prey. With good visual acuity at short range they move rapidly and silently through bush at considerable speed. At longer distance they can identify shapes like a hunter on the horizon but not so well against a low contrast background such as vegetation. I’ve glassed a prowling fox that seemed to walk past a rabbit crouching against a bush. Research suggests their visual system has low resolution, making the detection of small, stationary prey difficult in the absence of sound or scent.

In 1964, Finnish biologist Henrik Österholm published a paper in which he assessed the role played by the fox’s various senses during hunting. He concluded that vision is a key factor in finding food during daylight. It is less important at dusk and at night, when hearing was more vital. He concluded that hearing was the most significant sense, followed by vision and then smell.

Light is essential to the visual process and no animals can see in total darkness. Foxes have particular adaptations that allow them to be active at any time. They have vertically slit pupils that can be closed more tightly than round ones. Combined with eyelids that close horizontally, their eyes precisely adjust the amount of light entering their multi-focus eye, assisting hunting in a variety of light conditions.

The vertically slit pupil may help in identifying horizontal movement and improve the quality of vision in conditions of bright light. In a multi-focus eye, various colours of light are focused on different parts of the retina. A vertically slit pupil allows all the various zones to be used, even with the pupil reduced in size. Some colour perception is still possible

 

 

 

 

 

 

 

 

 

Significance of a slit pupil over a circular one. When a vertically (or horizontally) slit pupil contracts, light entering the eye is reduced but all wavelengths remain. (Diagram originally published in a 2006 paper by Tim Malmström and Ronald Kröger).

While the fox’s eye is an advantage in hunting, it’s also a weakness. The iris of the adult fox glows bright yellow under a spotlight due to a pigment called lipochrome. Spotlighting is a traditional and effective culling strategy. Humans lack a tapetum so in a flash photograph the light is reflected back by blood in the retina. This causes the ‘red-eye’ seen in many indoor photos.

Eyes contain rods and cones. Rod cells are sensitive to light and several rods can act together to stimulate a single neuron to send an electrical signal to the brain, which is used to build an image. However, the brain can’t tell which of the cells in the ‘rod bundle’ was stimulated, so it can’t interpret the exact size or shape of the object being looked at. Rods become saturated in light levels brighter than that produced by a 20-watt bulb. The rod system is a high sensitivity but low acuity system. It’s superb for letting the animal pick out objects in lowlight but the picture the animal sees lacks colour and detail.

Cones work in bright light and contain pigments that allow the perception of colour. Cone cells are less sensitive to light than rods, so more light photons must hit them before they are stimulated to send a message to the brain. They need relatively bright light to function, making them less useful at twilight or at night. They pick up more detail and detect rapid or subtle changes in an image that rods would miss.

Animals active during the day and night have a retina with a mix of rod and cone cells. The systems swap over as light levels rise and fall. The swap only takes seconds when cones take over from rods when moving from darkness to bright light. It is much slower when rods take over from cones when a light is turned off at night. The large number of rods along with the tapetum, give foxes much better night vision than humans have. They also have sufficient cone cells and a strictly controlled pupil that allow hunting during the daytime, even if the picture is less detailed or colourful than what we see.

Red foxes have a field of view spanning roughly 260 degrees, with a blind-spot covering about 100 degrees directly behind their head. Observations indicate foxes are short-sighted. They can easily run through vegetation but will approach stationary objects to within a few metres unless another sense alerts them to danger or the object moves.

In his book Town Fox, Country Fox Brian Vesey-Fitzgerald noted that fox eyes lack a macula lutea. This is the highly sensitive central part of the retina, responsible for our perception of detail. This implies that foxes are unable to focus on stationary objects for more than a few seconds, again rendering them short-sighted. Foxes have some binocular vision, less than humans but more than rabbits. This is useful for scaling fences and chasing down prey.

The optic axis of the fox (the angle the eyes look out relative to a line drawn down the middle of the body) is about 15 degrees. This means their eyes have difficulty converging on a near object as well as humans as our optical axis is 5 degrees. It’s been intimated that foxes use their eyes to avoid objects rather than recognise them.

Fox ears are very sensitive to low frequency sounds such as the rustling made by prey. There are two measures related to hearing that are important, the audible frequencies and the minimum audible angle (MAA).

Audible frequencies are the sounds that an animal can hear. Sound travels through the air in waves that peak and trough in a similar manner to waves on water, with one peak and trough considered a ‘cycle’. Sound is described based on the number of cycles per second.

Under ideal conditions, humans tend to be able to distinguish sounds moving by a single degree either side of them, while foxes have MAAs of about 14 degrees. In other words, humans can tell a sound is no longer ‘dead ahead’ when it moves to either side by only one degree, while the sound must move 14 degrees to either side before a fox would know it was no longer straight in front of them.

Foxes are often ‘called’ in from considerable distance using lures. This confirms the importance of sound to the hunting fox. Foxes also communicate over long and short distances with sound and use it to recognise possible danger. Vesey-Fitzgerald considered foxes to have better hearing than domestic dogs.

Behavioural experiments and field observations hint foxes have a keen sense of smell. We know that scent plays a crucial social function, being used to identify individual foxes and mark out territory boundaries. Additionally, authors have described how foxes have dug up carcasses of livestock buried several inches below the surface or covered by deep snow.

Population control of foxes uses various methods. 1080 baits can give cost effective results. While foxes are susceptible to this toxin, native Australian mammals are less so as it occurs naturally in some Australian plants. There is a downside. A reduction in fox numbers can result in increased feral cats. While cats are also susceptible to 1080 they rarely take baits. For some species, cats are just as significant a threat as foxes, or more so.

Fencing can exclude foxes from high-value areas such as nature reserves, although the investment needed to protect large tracts is significant. Livestock guardian dogs, such as the Maremma sheepdog, have proved useful in guarding livestock from predators such as foxes. They have also been used to keep foxes away from seabird colonies in southern Victoria.

There is evidence that dingoes can reduce populations of both foxes and feral cats, without eating the kill. This could be pure malice or maybe they are just fussy eaters. Whatever the reason, foxes and cats avoid dingoes, so where there are dingoes, foxes are less common.

To have the best effect on population size, trapping and shooting (including calling) are best done intensively in well-defined areas where rates of re-invasion are low. The foxes’ highly developed senses can also be managed by the hunter. Hearing can be negated by staying quiet. Working the wind can cancel out their sense of smell. Hides and camouflage assist in countering their vision. There doesn’t seem much point though, in dressing in the latest camo outfit while leaving hands or a face uncovered. To any animal, prey or predator, areas of skin flash a warning like a beacon.

It pays to understand the fox. Their senses will pick up the slightest mistake made by a hunter.

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